Preparation of 3D printable polyvinyl alcohol based conductive hydrogels via incorporating k-carrageenan for flexible strain sensors

Advances in conductive hydrogels are responding to the emerging need for flexible strain sensors. However, achieving an excellent combination of injectability, conductivity, and sensing characteristics is challenging. For this purpose, suitable 3D printing inks are required to generate hydrogels with the desired morphological and functional characteristics. We composited thermosensitive kC with PVA using borax as a cross-linking agent and a source of conductive ions (Na+) to obtain borax cross-linked PVA and kC conductive hydrogel inks. And then, the corresponding conductive hydrogels (B-PVA/kC) were successfully prepared using their thermal response behavior and freeze-thaw method. The results show that kC enables B-PVA/kC to undergo a rapid sol-gel transition when cooled from 70 °C to room temperature. The B-PVA/kC hydrogels show a fast, sensitive, and accurate response to movement. After a freeze-thaw cycle (1F-T), the hydrogels still have good electrical conductivity and strain-sensing properties, with better strength and increased structural stability. More excitingly, this hydrogel can be printed in different shapes to fit the body better and also exhibits good sensing signals when compressed by external forces, which is expected to facilitate the personalization of flexible strain sensors.